1. Field of the Invention
The present invention relates generally to electromagnetic devices and more particularly to a method for manufacturing electromagnets with plunger-type armatures and the structural design of such electromagnets.
2. Description of the Prior Art
Electromagnets of this kind are preferably used for the actuation of solenoid valves or other switching devices. They facilitate the actuation of the valve or switching device as a function of their state of excitation by attraction or release of a spring-loaded, plunger type armature.
In general, electromagnets with plunger-type armatures, and especially such electromagnets as are employed in solenoids for washing machines, are provided with a coil form made of a suitable plastic material onto which is applied the copper wire coil winding. Subsequently, the position of the coil winding is protected by a plastic cover. The elements forming the magnetic circuit are assembled on the covered coil winding. In general, prior art electromagnets comprise a magnetic back circuit surrounding the coil and two, preferably cylindrical, hollow bodies which join both ends of the magnetic back circuit and continue on both sides into the interior of the coil.
This prior art manner of production of an electromagnet exhibits several shortcomings. For example copper wire used for the coil winding on the coil form must have sufficient strength so that it does not become deformed during or after the winding or, even worse, break. For this reason, the inner wall of the coil form must have sufficient thickness and strength. This, in turn, results in the placement of even inner windings of the coil at a sufficiently large distance from the magnetic elements in the interior of the coil form which leads to an additional magnetic loss. On the other hand, the magnetic back circuit which must be applied after the plastic sealing must be very large in volume in order to encircle the cast-on mass. All of this resulted in comparatively heavy and bulky prior art magnetic systems.
The two cylindrical hollow bodies within the coil opening must be rigidly connected with the magnetic back circuit in order to ensure good support and favorable magnetic properties of the complete circuit. This, in turn, necessitates very precise adjusting tolerances of all parts relative to one another. Moreover, the fastening means cause additional increase of the distance between the magnet elements and the coil wire, resulting in a further loss of magnetic energy and additional needs of material, especially copper wire in the prior art devices.